Tamper-proof seal system

ABSTRACT

A seal system which comprises a seal, preferably a two part capsule with an internal closure clip, made from a base material containing a random non-homogeneous mixture of foreign substances, enabling the identity of the seal and damage to it to be determined spectrographically by a non-destructive apparatus for detecting X-ray fluorescence.

Uite States atet [191 Jehenson et a1.

[ Mar. 4, 1975 [73] Assignee: European Atomic Energy Community (Euratom) 22 Filed: Aug. 3, 1972 21 App1.No.:277,606

[52] U.S. Cl. 250/272, 250/274 [51] Int. Cl. G01n 23/22 [58] Field of Search 250/272, 273, 274, 275,

[56] References Cited UNITED STATES PATENTS 2,901,629 Friedman 250/273 3,197,638 7/1965 Sinclair 250/274 Primary E.\'aminer-.lames W. Lawrence Assistant E.\'aminer-C. E. Church Attorney. Agent, or FirmStevens, Davis, Miller & Mosher [57] ABSTRACT A seal system which comprises a seal, preferably a two part capsule with an internal closure clip, made from a base material containing a random non-homogeneous mixture of foreign substances, enabling the identity of the seal and damage to it to be determined spectrographically by a non-destructive apparatus for detecting X-ray fluorescence.

2 Claims, 4 Drawing Figures 7 40 GRAPHICAL RECORDER 44 RADIATION or Rgglggfi COMPUTER m RECEPTOR k 36 1 0: A o DIGITAL CONVERTER RECORDER t -1 38 Q SEAL PRINTER PEER [EU W 4 COMPUTER DIGITAL RECORDER PRINTER GRAPHICAL RECORDER ANALOG RECORDER RRDIATION RECEPTOR A D CONVERTER RADIATION FIG.3

TAMPER-PROOF SEAL SYSTEM FIELD OF THE INVENTION The invention relates to a tamper-proof seal system in which foreign substances are provided in the base material of the seal and in which a non-destructive reading apparatus is provided which responds to the foreign substances.

BACKGROUND OF THE INVENTION A seal should be an object which can be reproduced only with difficulty and is therefore employed to secure plants and the like against unauthorized access. Seals are particularly effective if the property which defines the reproducibility of such seals is obtained during the production of the sea] by virtue of a random event. For example, this applies to seals of the kind described in Atomwirtschaft, August, 1970, page 375, where short pieces of metal wire are admixed in random distribution in the base material of the seal. The identity of the aforementioned seal would then be obtained from a picture of the seal, recorded for example by optical or X-ray apparatus.

Location of the foreign substance particles by means of ultrasonic reflection is well suited to practical conditions because this method enables the identity of an encapsulated seal, comprising two parts, to be defined before the seal is assembled at the security location. This advantage however does not mean that the method requires no portable reading apparatus because it is often desirable to test the identity of an undamaged seal without the need for removing and renewing the seal. The development of portable ultrasonic reading apparatus for seal systems however has shown that an acceptable degree of accuracy in the location of the enclosed particles can be achieved only at considerable expense.

SUMMARY OF THE INVENTION The invention is to avoid this disadvantage without any loss of security against tampering. The last mentioned restriction means that only those properties for characterizing the seal may be considered which'cannot be influenced from the exterior and which are created randomly during manufacture of the seal. It is known practice to ascertain the position of foreign matter. By contrast, the seal system according to the invention is characterized in that particles of a plurality of different substances (in particular metals and alloys) are used as foreign substances and are admixed into the base material of the seal in a random, nonhomogeneous distribution and that the reading apparatus comprises an X-ray fluorescence measuring apparatus which defines the global fluorescence spectrum of at least one surface of the seal..

A seal system in the sense used herein therefore comprises a seal with a variable identification quantity and reading apparatus for defining this quantity. In the present case the variable quantity is the spectrum which is measured by X-ray fluorescence measuring apparatus. Basically, the material composition of the seal is spectrographically tested but because of the nonhomogeneous distribution of the inclusions the spectrum dose measured is well defined but differs from the actual integral composition of the seal. If the seal is irradiated from different sides a different spectrum will be obtained for each side owing to the relatively slight LII penetration depth of the energizing X-rays. Without defining the position of the individual inclusions in this method, the random position thereof affects the measurement. The fact that measurement covers an entire side in a single global measuring operation instead of one'surface being scanned, point by point, means that the reading apparatus according to the invention is able to function with a minimum of mechanical effort and may therefore be embodied in portable apparatus with a relatively high degree of accuracy.

According to another aspect of the invention a seal comprises a base material containing a plurality of randomly distributed foreign substances enabling the identity of the seal or damage to it to be established spectrographically.

The seal preferably takes the form of a two-part capsule, adapted to be irreversibly closed by means of internally disposed retaining means such as books. A construction of this kind has already been proposed for ultrasonic seal systems; in that system as well as in the present system it ispossible for the identity of the capsule to be defined both in the opened as well as in the closed state. Since the inventive seal system does not scan the seal surface point by point but measures the entire surface unit integrally, it is particularly advantageous to provide the capsule in the closed state thereof with clearly defined surface shapes which can be easily scanned by the reading apparatus. In this case the cylindrical shape is selected as an example since it is convenient to make.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a capsule of the kind which may be used asa seal in the seal system according to the invention; and

FIGS. 2 and 2a show two sectional views of the afore mentioned seal; and

FIG. 3 shows a seal identifying apparatus for use with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The seal according to FIG. 1 comprises two capsule parts 1 and 2, irreversibly joined to each other by means of an internally disposed clip 3, visible in FIG. 2. The clip joins the cylindrical edge of the capsule half 2, completely surrounded by the surface part of the other capsule half 1, with a mushroom-shaped central part 4 the base of which is secured to the capsule half 1 by means of a frangible web. In the event of an attempt at forcible opening, the central part breaks in this region and produces a fracture line which, even after repair, is recognized as a deviation from the original identity by the reading apparatus. The central part 4 is of rectangular cross-section to achieve a defined angular position of the two capsule halves which are otherwise rotationally symmetrical. However, the same objective may be achieved by means of noses or grooves in the surfaces which are in physical contact with each other.

The central part is also provided with two apertures 5 which extend into the interior 6 of the seal and through which the two ends of a seal band are introduced and knotted in the interior space. Aluminum, steel, zirconiumor a plastic may be used for the two capsule halves. Apart from other conditions (compatibility with ambient conditions) it is essential to ensure that the material is only slightly absorbent to X-rays when such materials are selected. During manufacture, for example in a process of powder metallurgy, a defined number of different chemical elements, in particular metals, in the form of small particles such as chips are distributed in the aforementioned material. The chemical elements iron, niobium, copper, nickel, zirconium, tungsten, lead, silver or tin may be used to this end. The following enclosed particles, referred to hereinbelow as foreign substances, are illustrated as dots in FIG. 2. The distribution of the foreign substances (i.e.,

different from the base capsule material) is very inhomogeneous and therefore impossible to reproduce: it is practically impossible to produce artificially a seal whose X-ray spectra on all sides conform to that of a pattern seal.

The identity of the seal is obtained from the selectable characteristics of the spectra recorded on the individual surfaces of the enclosed capsule. Owing to the slight penetration of X-rays the individual spectra will be defined in practice only by the foreign substance particles in the zones of the seal nearest the surface. To this end it is by no means necessary for all possible sides of the capsule to be scanned if the spectra of one or a few surfaces provide sufficient data for unmistakable identity. It is therefore advisable to select in particular surfaces whose identity would change if the seals were to be cut or otherwise opened for the purpose of forgery.

FIG. 3 shows an X-ray reading apparatus for use in scanning and then identifying seals, such as those of the present invention, and for verifying the identity of'the seals on the basis of information recorded in a library.

The apparatus consists of a source of radiation (X-rays, gama rays, etc.).30, an X-ray fluorescence receptor 32 which receives radiation transmitted by the seal which is excited by the source 30. The receiver 32 generates a voltage output proportional to the received radiation, which output is fed to one more ofa graphical recorder 34, an analog recorder 36 and an analog/digital converter 38. The graphical recorder produces a graph representative of the identity of the seal: this graph is then stored directly in the library 40. Alternatively, the output of receiver 32 may be applied through the analog recorder 36 or the A/D converter 38 and a digital recorder 42 to a computer 44, the print out, paper tape, punch cards, etc., is then stored in the library 40. Alternatively, the output from the A/D converter 38 may be applied correctly to a printer 46 whose output isstored in the library.

In a practical embodiment, the measuring means (the source-receiver and one of the aforementioned recording devices) can be contained in a portable or a transportable unit for on-sight inspection of the seal. When a seal is inspected, the recorded measurement of the particle distribution is compared with a similar previously made measurement of the same seal (generally before use) in order to determine whether or not the seal has been tampered with, as by the substitution of a different seal.

The reading apparatus is provided either with a wide, effective aperture which completely covers the surface to be scanned or it is provided with only a narrow scan ning slit 33 under which the seal is moved by means 31 at defined velocity, the part spectra being integrated with respect to time to form a global spectrum of the entire surface area so scanned and integrated. The last mentioned method is used preferably for endless surfacessuch as the external surfaces of the aforementioned cylindrical seal. However, finite, plane surfaces such as the endfaces of such a seal may also be scanned in this manner by using a scanning slit which has the form of a circular sector.

If the surfaces of the seal which must be scanned also include the joined surfaces between the two capsule surfaces in this example the external surface it is not possible for the identity of the seal to be defined only by the partial identities of the two halves. In order to establish the identity of the seal before attaching same to the object to be secured, the seal halves are assembled without the clip 3 and the joined surfaces are then measured. Constructive or other measures (marking) must then ensure a clearly defined rotational position of the two parts relative to each other which position will also correspond to the rotational position after attachment of the seal. This dispenses with the need to use the reading apparatus when the plant is sealed.

Tests have shown that scratches in the surface of the seal vary the measured results only slightly and within acceptable limits. However, it has been found advantageous to degrease the seals prior to measurement in an organic cleaning agent. To improve the measuring accuracy it is also advantageous to compare the measured spectra with a characteristic line of the energizing X-ray tube itself.

The X-ray apparatus could also be replaced by an isotope source. This is more difficult to transport,

owing to the required shielding, but offers the advantage of a better resolution and higher sensitivity for heavy foreign substance-elements.

The invention is not confined to the capsule form illustrated in the drawing but may also be applied to seals which are constructed integrally. The mating piece with which the seal is joined in practice is a structural element of the plant to be secured and not marked with foreign substances, for example a retaining bolt for the mesh plate in which the fuel elements of a nuclear reaction are retained. Constructive measures may prevent the unmarked part of the retaining bolt being severed and then welded together again for the purpose of tampering.

What is claimed is: l. A spectrographically identifiable security seal system, comprising:

at least one security seal comprising a base material containing particles of a plurality of different, spectrographically identifiable substances different from said base materials randomly mixed and nonhomogenously distributed within said base material, 1

said seal comprising a two-part capsule including internal retaining means for irreversibly closing said capsule,

and non-destructive spectrographic reading means for detecting damage to said security seal, said reading means including X-ray fluorescence measuring means for determining the spectrum of at least one surface of said seal, and comparing said spectrum to a previously recorded spectrum of said seal.

2. A seal system according to claim 1, in which the reading means comprises a narrow effective scanning slit, rotary means for traversing said surface under the the entire surface area of said seal member. 

1. A spectrographically identifiable security seal system, comprising: at least one security seal comprising a base material containing particles of a plurality of different, spectrographically identifiable substances different from said base materials randomly mixed and non-homogenously distributed within said base material, said seal comprising a two-part capsule including internal retaining means for irreversibly closing said capsule, and non-destructive spectrographic reading means for detecting damage to said security seal, said reading means including Xray fluorescence measuring means for determining the spectrum of at least one surface of said seal, and comparing said spectrum to a previously recorded spectrum of said seal.
 2. A seal system according to claim 1, in which the reading means comprises a narrow effective scanning slit, rotary means for traversing said surface under the scanning slit, and integrating means responsive to said spectrum for obtaining a spectrum of said spectrum of the entire surface area of said seal member. 